1. Field of the Invention
The invention relates to a focus monitor method and mask suitable to setting focus conditions in a projection exposure apparatus relevant to the manufacture of semiconductor devices and LCD devices and the like.
2. Description of the Related Art
Among techniques of measuring a defocus amount with high accuracy and simplicity, a method as described hereinafter is known (for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-100392). According to this technique, a focus monitor mask in which a pattern (focus monitor pattern) capable of detecting focus variations is disposed, a line width of a post-transfer monitor mark is measured by using a linewidth measuring apparatus (optical linewidth measuring apparatus, such as an SEM or the like) or a linewidth measuring functionality built in an exposure apparatus itself, a variation amount of focus is obtained thereby.
According to the focus monitor pattern described in the above patent publication, the defocus amount independently from exposure can be measured even when the exposure. However, depending on a set exposure, a sensitivity of calibration curve can undesirably varied due to the exposure. The set exposure is set by a layer of a device. However, when a large difference takes place between set exposures for layers, there can occur a case in which the large deviation from an optimal exposure for the focus monitor pattern (the exposure range in which exposure dependency is law in the calibration curve). To address such a problem, it is ideal to optimally design the focus monitor pattern by the layer. However, the creation of the pattern is a time-and-cost consuming process, so that a more simple technique has been demanded.
As described above, the technique gives rise to the problem in that when exposure is performed with the exposure largely deviating from the optimal exposure for the focus monitor pattern, the exposure dependency takes place in the calibration curve, resulting in a large tolerance of the amount of the defocus to be obtained.